This project examines the hypothesis that contact-lens-induced stromal acidosis causes permanent changes in corneal structure and function. Studies have now been completed which provide preliminary evidence that corneal acidosis alters cell morphology, reduces corneal hydration control, and slows corneal recovery after induced edema. These results also suggest that contact-lens-induced stromal acidosis may alter corneal integrity, and therefore it is important to explore in some depth the pH- mediated effects that result from CL wear. To study these effects, it was necessary to find the critical lens oxygen transmissibility (Dk/L) for avoiding stromal acidosis under closed-eye contact-lens-wearing conditions. Having determined this critical Dk/L value, we now propose to study the development and reversibility of corneal changes that result from corneal acidosis induced by extended contact lens wear. The experimental design provides for 2 extended-wear groups with identical fitting characteristics except that one lens type lowers corneal pH while the other lens type does not affect corneal pH. Regular assessments of corneal structure and function will be made during a 2-1/2 yr. lens- wearing phase followed by a 3-month period in which contact lens wear is discontinued. Using this paradigm, it will be possible to assess the impact of reduced corneal pH resulting from extended wear on the development and reversibility of contact lens induced keratopathies. The information obtained from this study will further our understanding of the nature and etiology of corneal complications resulting from contact lens wear, improve present contact lens treatment strategies, develop guidelines for elimination of those lens wearing conditions where stromal acidosis is likely to place the contact lens patient "at risk," and provide quantitative data on the effects of changes in extracellular pH on corneal structure and function.